The present invention relates to a method and apparatus for controlling a vehicle air conditioner for controlling air-conditioning air.
As described in Japanese Patent Publication No. 62-8327, in a control method for a vehicle air conditioner, the outlet air flow rate and the outlet air temperature of air-conditioning air are controlled while balancing between the heat amount supplied from an air conditioner into a passenger room, and the heat load acting on a vehicle. As will be described in detail later, the fundamental equation of air-conditioning control during an unstable period is given by: EQU Cp.multidot..gamma..multidot.V.sub.a (T.sub.o -T.sub.SET)=K.multidot.S(T.sub.SET -T.sub.a)-K.sub.s .multidot.T.sub.s -C+K.sub.i .multidot.(T.sub.SET -T.sub.r)
In this control equation, the left-hand side represents the heat amount to be supplied from the air conditioner into the passenger room, and the right-hand side represents the vehicle heat load. In the equation, T.sub.SET is the setting temperature, T.sub.a is the atmospheric temperature, and T.sub.r is the passenger room temperature.
In the air-conditioning control, the outlet air flow rate V.sub.a and the outlet air temperature T.sub.o are set on the basis of the above-mentioned heat balance equation. In this case, however, two unknowns V.sub.a and T.sub.o cannot be uniquely obtained from a single equation.
In the technique described in the above-mentioned patent publication (Japanese Patent Publication No. 62-8327), the relationship between an environmental condition such as the atmospheric temperature, and the like, and the outlet air flow rate V.sub.a is determined in advance, and an outlet air flow rate V.sub.a corresponding to the detected environmental condition is preferentially determined. The determined outlet air flow rate V.sub.a is substituted in the heat balance equation to obtain the outlet air temperature T.sub.o.
On the other hand, Japanese Patent Laid-Open No. 2-120117 describes the following technique. That is, the outlet air temperature T.sub.o is set by a passenger, and is substituted in the heat balance equation to obtain the outlet air flow rate V.sub.a.
In the air-conditioning control, air-conditioning air is controlled, so that the passenger room temperature T.sub.r eventually becomes equal to the setting temperature T.sub.SET. For example, in terms of comfort, air-conditioning air is controlled to be lower than the setting temperature T.sub.SET in the summer, and contrary to this, air-conditioning air is controlled to be higher than the setting temperature T.sub.SET in the winter. From this viewpoint, Japanese Patent Laid-Open No. 57-77216 discloses a technique for changing a target temperature in air-conditioning control according to the atmospheric temperature under a condition that the air-conditioning control is made based on the above-mentioned heat balance equation.
The ultimate object of an air conditioner is to provide comfort to passengers, and the comfort felt by a passenger is a combination of various factors. Therefore, when the outlet air flow rate V.sub.a is preferentially determined according to an environmental condition, and then, the outlet air temperature T.sub.o is determined like in the above-mentioned prior art, it is unknown whether or not a combination of the determined outlet air flow rate V.sub.a and outlet air temperature T.sub.o can give the best comfort to a passenger in that specific case.
Similarly, when the outlet air temperature T.sub.o is set by a passenger, it is not always certain whether or not the outlet air temperature T.sub.o set as a desirable temperature by the passenger can give the best comfort in association with the outlet air flow rate V.sub.a. Of course, when the set outlet air temperature T.sub.o is not desirable in association with the outlet air flow rate V.sub.a, the passenger need only change the outlet air temperature T.sub.o. However, this forces an extra operation load on a passenger.
Furthermore, when the target temperature of air-conditioning control is changed according to the atmospheric temperature, it is unknown whether or not the changed target temperature can give the best comfort to a passenger in association with the outlet air flow rate V.sub.a.
The above-mentioned problems are always posed during air-conditioning control. Besides these problems, various other problems are posed when an engine is started from a state wherein the engine stands still, and air-conditioning control is initiated.
For example, as a method of solving the problems posed when air-conditioning control is started, as described in Japanese Patent Publication No. 62-5371, the operation of a blower is started when the temperature of an evaporator is decreased to a predetermined temperature, i.e., the outlet operation of air-conditioning air is delayed, so as to prevent hot air in a duct from being exhausted from an outlet port into a passenger room when a cooling operation is started.
For example, assume a vehicle under the blazing sun. A passenger who gets on such a vehicle wants wind at once in any case. However, when air-conditioning air is output upon start of the cooling operation, hot air in a duct is output from the outlet port, as described above, thus enhancing discomfort.
On the other hand, in addition to the problem posed when the cooling operation is started, a problem is also posed when a heating operation is started in the winter.
For example, a water-cooled engine normally uses engine cooling water as a heat source of heating. For this reason, sufficiently warm air cannot be supplied into the passenger room in heating control during a warm-up operation before the engine cooling water is sufficiently warmed.
In association with heating control during the warm-up operation, Japanese Patent Laid-Open No. 60-29319 discloses the following technique. That is, an air outlet mode is changed according to the temperature of engine cooling water. Japanese Patent Publication No. 1-20084 discloses the following technique. That is, when the temperature of engine cooling water is low, a defrosting mode is set, so that cold air-conditioning air does not directly blow against a passenger. On the other hand, when the temperature of engine cooling temperature is increased to a medium temperature, a defrosting/heating mode is set. When the temperature of engine cooling water is increased to a high temperature, a heating mode is set. Japanese Patent Publication No. 60-21082 discloses a technique wherein the outlet air flow rate is increased according to the temperature of engine cooling water.
Comfort felt by a passenger upon blowing of air-conditioning air into the passenger room does not always depend on only the temperature of air-conditioning air. More specifically, if the passenger room temperature is extremely low, even when the defrosting/heating mode is set after the temperature of engine cooling water is considerably increased, cold air in the passenger room is stirred by air-conditioning air output from both a defroster outlet port and a foot outlet port, and for this reason, the passenger may feel rather cold.